This project is directed towards development and testing of a liposomal adjuvant system which will engender a strong and sustained immune response to antigens of low immunogenicity. This adjuvant system will consist of liposomes which contain one or more non-toxic immunopotentiators of microbial origin. These immunopotentiators are highly active as adjuvants when administered in oil-in-water emulsions. Two possible modes of antigen incorporation, encapsulation and covalent attachment, will be evaluated. The performance of liposomal adjuvants with both a polysaccharide and a peptide antigen will be assessed, in order to establish the general utility of this approach. Several immunological criteria will be used for evaluating the effectiveness of these liposomal vaccines: (1) the magnitude of the humoral and cell-mediated immune responses; (2) the distribution of antibody classes and IgG sub-classes; and (3) the response to secondary immunizations (immunological memory). The ability of these liposomal vaccines to stimulate non-specific resistance against an antigenically-unrelated pathogen will also be evaluated, using a murine bacterial challenge model. An adjuvant system which is safe, non-toxic, and which can stimulate a strong immune response to antigens of low immunogenicity would be of considerable interest to producers of vaccines. Antigens produced by synthetic or recombinant techniques could be combined with such an adjuvant system to produce safer and more effective vaccines than are currently available.